Lignin Films from Spruce, Eucalyptus, and Wheat Straw Studied with Electroacoustic and Optical Sensors: Effect of Composition and Electrostatic Screening on Enzyme Binding

Lignins were isolated from spruce, wheat straw, and eucalyptus by using the milled wood lignin (MWL) method. Functional groups and compositional analyses were assessed via 2D NMR and 31P NMR to realize their effect on enzyme binding. Films of the lignins were fabricated and ellipsometry, atomic force microscopy, and water contact angle measurements were used for their characterization and to reveal the changes upon enzyme adsorption. Moreover, lignin thin films were deposited on quartz crystal microgravimetry (QCM) and surface plasmon (SPR) resonance sensors and used to gain further insights into the lignin–cellulase interactions. For this purpose, a commercial multicomponent enzyme system and a monocomponent Trichoderma reesei exoglucanase (CBH-I) were considered. Strong enzyme adsorption was observed on the various lignins but compared to the multicomponent cellulases, CBH-I displayed lower surface affinity and higher binding reversibility. This resolved prevalent questions related to the affinity of this enzyme with lignin. Remarkably, a strong correlation between enzyme binding and the syringyl/guaiacyl (S/G) ratio was found for the lignins, which presented a similar hydroxyl group content (31P NMR): higher protein affinity was determined on isolated spruce lignin (99% G units), while the lowest adsorption occurred on isolated eucalyptus lignin (70% S units). The effect of electrostatic interactions in enzyme adsorption was investigated by SPR, which clearly indicated that the screening of charges allowed more extensive protein adsorption. Overall, this work furthers our understanding of lignin–cellulase interactions relevant to biomass that has been subjected to no or little pretreatment and highlights the widely contrasting effects of the nature of lignin, which gives guidance to improve lignocellulosic saccharification and related processes.

Publication year: 2017
Authors: Pereira A. 1,2, Hoeger I.C. 2, Ferrer A. 2 , Rencoret J. 1, del Rio J.C. 1, Kruus K. 3§, Rahikainen J. 3, Kellock M. 3, Gutiérrez A. 1, Rojas O.J. 2,4
Affiliations:
1 – Instituto de Recursos Naturales y Agrobiología de Sevilla (IRNAS), CSIC, Avenida de la Reina Mercedes, 10, E-41012 Sevilla, Spain
2 – Departments of Forest Biomaterials and Chemical and Biomolecular Engineering, North Carolina State University, Raleigh, North Carolina 27695, United States
3 – VTT Technical Research Centre of Finland Ltd, P.O. Box 1000, FI-02044 Espoo, Finland
4 – Department of Bioproducts and Biosystems, School of Chemical Engineering, Aalto University, FI-00076 Espoo, Finland
Published in: Biomacromolecules, 2017, Vol. 18 (4), p. 1322–1332
DOI: 10.1021/acs.biomac.7b00071

MP-SPR KEYWORDS

adsorbed mass electrostatic interaction enzyme adsorption enzyme-lignin interaction ionic strength lignin - cellulase interaction QCM spruce lignin to improve lignocellulosic saccharification wheat straw lignin
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